Vapor deposition apparatus

ABSTRACT

A vapor deposition reactor having a gaseous phase inlet and exit system including inlet means, located at one end of a reaction chamber, including a porous gas distribution baffle which forms a plenum and which uniformly delivers gaseous materials to substantially all of the horizontal cross-sectional area of the reaction chamber and further including an exit means, located at the other end of the chamber, comprising a porous pressure baffle for uniformly allowing the removal of gaseous materials from the chamber to prevent recirculation of reaction byproducts.

United States Patent [72] Inventor Richard R. Garnache South Burlington,Vt. [21] Appl. No, 344 [22] Filed Jan. 2, 1970 [45] Patented Sept. 7,1971 [731 Assignee International Business Machines Corporation Armonk,N.Y.

[54] VAPOR DEPOSITION APPARATUS 10 Claims, 1 Drawing Fig.

[52] U.S.Cl 118/48 [51] lnt.Cl .j C23c 11/00 [50] Field of Search 118/4849.5; 117/106-1072 R, 107.2 P, 106 R,

[56] References Cited UNITED STATES PATENTS 2,378,476 6/1945 Guellich118/49 2,489,127 11/1949 Forgue 117/106 R Primary Examiner-Morris KaplanAttorneys-Hamlin and J ancin and Howard J. Walter ABSTRACT: A vapordeposition reactor having a gaseous phase inlet and exit systemincluding inlet means, located at one end of a reaction chamber,including a porous gas distribution baffle which forms a plenum andwhich uniformly delivers gaseous materials to substantially all of thehorizontal cross-sectional area of the reaction chamber and furtherincluding an exit means, located at the other end of the chamber,comprising a porous pressure baffle for uniformly allowing the removalof gaseous materials from the chamber to prevent recirculation ofreaction byproducts.

PATENTEU SEP' 7 19m 3 03 2 INVENTOR RICHARD R. GARNACHE BY WM MM AGENTtOI'.

meager VAiPllllll lii lilll tlSll'llllflN APPARATUS This inventionrelates to vapor transport chemical vapor deposition processes, and moreparticularly, to an improved apparatus for carrying out these processes.

BACKGROUND As is well known in the art, vapor transport chemical vapordeposition reactions have many applications in the area of semiconductorand other solid state device manufacturing. in essence, any heat inducedgar/court reaction producing desirable byproducts might be utilimd.

Many ditfcrent processes and reactions have been used in what isgenerally tenned vapor growth; for example, various pyrolytic anddisproportionation reactions have been em ployed, in addition to thewell-known epitaxial semiconductor deposition process, for thedeposition of oxides, nitrides, and metals. One of the most frequentlyused of these already developed processes is one involving the hydrogenreduction of silicon tetrachloride at an elevated temperature.

One object of many chemical vapor deposition systems is to produce auniform product. ll uniform products cannot be produced, great expenseis entailed either by redesigning device specifications to fit thevariations of the product produced or by the rejection of a largepercentage of the products.

The problems which have been faced previously in chemical vapordeposition processes include: contamination of the reaction chamber;lack of uniformity of deposit thickness on all substrates in a singlereaction vessel, as well as individual substrates; the presence ofspikes on the surface of the sub strates; and long cycles involved inthe batch operations currently employed.

lPlRllOR ART of such a reactor is disclosed in US. Pat. No. 3,424,629,to

Ernst et al., issued .lan. 28, 1969,2md assigned to the assignee of theinstant invention. W

The barrel reactor consists of a barrellihe chamber which contains acylindrical susceptor upon which a number of sub strates may be mountedcircumferentially. Gaseous reactants admitted at the bottom of thereactor by a halo-shaped inlet system are passed over the substratesurfaces, usually heated by an externally located RF coil. Exhaust gasesare removed from the reactor through a port located in the top of thereaclllowever, the barrel reactor did not solve all of the problemsfound in the prior art. The primary advantage of the barrel reactor wasto increase batch sizes over the open tube method. Deposits produced inbarrel reactors still had many drawbacks. For example, dust particlecounts as high as 100,000 particles per it, could easily causecontamination of substrates. Film thickness variations on the order of i0.5 microns on a single wafer are also common. Other problems such asthe presence of op xia these e often found.

it is therefore an obje t of this inve tion to improve the quality ofvapor deposition products and the operating characteristics of barrelreactors in general by decreasing the duty cycle required to performeach batch operation.

Another object is to reduce the contamination level in deposited filmsby reducing the dust count inside the reactor.

A further object of this invention is to provide more uniform chemicalvapor deposition deposits.

A still further object of this invention is to substantially reduce oreliminate the number of spikes formed in deposited films.

SUMMARY OF THE INVENTION Briefly considered, the reactor of the presentinvention is constructed to realize the aforementioned objects, goalsand advantages and comprises a barrel reactor having a gaseous phaseinlet system including a gas distribution baffle extending substantiallyacross the entire horizontal cross-sectional area of the reactionchamber which provides uniform distribution of reactants entering thechamber and a planar velocity front substantially throughout thechamber. An exit pressure baffle also extending substantially across theentire horizontal crosssectional area of the chamber is utilized tomaintain a constant mass flow from the chamber and to preventrecirculation of the gaseous products leaving the chamber.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawing.

The FlGUlRE shows a partial sectional view of a preferred embodiment ofthe present invention.

DETAELED DESCRlPTlON The reaction that is illustratively employed todemonstrate the preferred embodiment is the reduction of silicontetrachloride by hydrogen, described by the equation:

SiCll,,+2ll-2l Heat Si +4HCL. (i in actuality the reaction is morecomplex and depends upon the reactant concentrations, temperature,pressure, and reactor geometry, all of which may result in various sidereactions. Since the reaction is reversible, etching and mass transportprocessing may also occur.

Although the method and apparatus of the present invention will bedescribed in the specific context of the above reaction, it will beapparent to those skilled in the art that other vapor transportreactions may be similarly utilized. Thus, the apparatus of the presentinvention is not. Tied to a single reaction or process since the onlylimiting criteria for advantagco-us application of the instant apparatusis that a reducible vapor source, or a heat induced chemical reactionbyproduct be available. For example, the following types of reaction arepossible: disproportionation, decomposition, condensation and gascracking. Additionally, since a number of such reactions are reversible,the removal offilms, or material, from substrate surfaces, as well asthe deposition of material, is possible. Thus, reference to vapordeposition processes in describing the instant invention may also beconsidered to include any heat induced chemical vapor deposition oretching process.

Referring to the FIGURE, there is shown a partial sectional view of avapor deposition reactor, generally designated ill), comprising anopaque quartz cylinder 112, which is capped at both ends by hollowplates M and lid made of stainless steel, through which cooling watermay be circulated, by means not shown, defining a reaction chamber ill.The reaction chamber may, for example, be 9 inches in diameter and 18inches high. Tie rods 2b, with the aid ot'G-rings 22 and 2d, enablechamber id to remain airtight during the vapor deposition process. Thelower plate lb and O-ring 2d, are attached to a hydraulic cylinder (notshown) which opens and closes the reactor. Situated within the reactionchamber iii, and mounted on a fusedquartz rod 16 is a substrate holder,graphite susceptor 2d, having mounted around its circumference, andsubstantially parallel to the chambers longitudinal axis, as defined byrod 2a, a plurality of substrates Illl upon which deposition is desired.The susceptor may he cut from commercially available high puritygraphite and is substantially in the form of a hollow right cylinderhaving a wall thickness of about three tribution in the reaction chamber18.

eighths inch. The substrate holder is preferably tapered about 3 frombottom to top and is counterbored in order to provide recesses tosupport substrates. The susceptor may be mounted on rod 26 by a starplate.

Supported by the top plate 14 and extending across the horizontal crosssection of the chamber, there is provided a gaseous phase inlet meansincluding a gas distribution baffle 38 forming, with plate 14, a firstplenum 36. Gaseous phase materials, reactant gases SiCl4 and H2,generally designated by arrow 32, are introduced through tube 34 intothe plenum 36. Plenum 36 and gas distribution baffle 38 together providea means for evenly delivering the reactant gases 32 over substantiallyall of the horizontal cross-sectional area at the top of the reactionchamber 18. Gas distribution baffle 38 may be constructed from aperforated plate or a sintered material having a gas resistancesufficient to develop substantially uniform back pressure to maintaineven gas distribution over the entire surface area of the baffle, andthg eby deliver a uniform rna ssiflowinto substantially theentirehorizontal cross-sectional area a the chamber 18. Baffle 38 may beone-.eighth inch thick sintered stainless steel filter plate having anaverage pore size of microns. Additionally, gas distribution baffle 38may be a perforated metal plate providing that the proper number andsize holes may be provided to achieve the desired pressure drop and gasdis- Also shown is a heat shield 40 which may be mounted on the reactionchamber side of gas distribution baffle 38. The purpose of heat shield40 is to reflect energy radiated from the heat shield 40 is to reflectenergy radiated from the heated susceptor 28 which may prove harmful tobaffle 38, depending upon the material of which the baffle isconstructed. Heat shield 40 is merely a thin stainless steel, ormolybdenum plate, about 0.040 inch thick, having a number of 0.08 l-inchdiameter holes 41 drilled on 0.25-inch centers. The plate is constructedsuch that it will not substantially disturb the gas flow through thechamber but will effectively prevent baffle 38 from overheating andperhaps out-gassing or decomposing. It should be understood that theaddition of heat shield 40 is merely optional as it is used, or notused, depending upon the temperature at the top of the reaction chamberand the material of which gas distribution baffle 38 is made. u

The gaseous materials, after passing through heat shield 40, enterchamber 18 having a planar velocity fronti.e., the gas velocity at allpoints on a horizontal cross-sectional area of the chamber is constant.Because susceptor 28 is a thin walled cylinder and substrates 30 aresubstantially flush with the outer surface of the susceptor, littleresistance is met by the gas as it passes over susceptor 28. Thus, asubstantially planar velocity front is maintained throughout the lengthof chamber 18.

After passing over the susceptor 28, reactant gases leave the bottom ofthe chamber 18 through the following means. Mounted in the bottom of thereaction chamber, and extending across substantially the entirehorizontal cross-sectional area of the chamber is a gaseous phase exitpressure baffle 42 which like gas distribution baffle 38 may be made ofa sintered or porous material. Although it is desirable to provide thesame pressure drop across exit pressure baffle 42 as that provided bygas distribution baffle 38, it is preferable that the porosity of baffle42 be greater than baffle 38. The reason for this is twofold; first,because various deposits may tend to form in the pores of exit pressurebaffle 42 thereby gradually increasing its resistance to gas flow, andsecond, because it is important only to maintain the planar velocityfront until the gaseous materials have passed the susceptor. it is onlynecessary to maintain a pressure drop across exit pressure baffle 42.Therefore, the gas resistance presented by baffle 42 is substantiallyless than that of gas distribution baffle 38, on the order ofone-twentieth. This may be achieved by utilizing a perforated plate, orsintered material, that is more porous, or less dense, than utilized atthe inlet of the chamber. Pressure baffle filame t 2", beg n Pl .9."? nmeivsskx sass and 46. Exhaust gases are passed from a second plenum 48through exhaust tubes 50 and delivered to the atmosphere or areclamation process.

In order to raise and maintain the temperature of the substrate surfacesto the proper reaction temperature, a heating means is required. An RFsource is preferred, Although a resistance heater may also be used. AnRF generator, not shown, is used to inductively heat susceptor 28 to therequired temperatures. The generator is coupled to a water-cooledhelical coil 52 which is permanently positioned outside quartz cylinder12. It will be noted that this arrangement of a cylindrical load coupledto the helical RF coil 52 provides excellent heating efficiency Sinceall pointson the circumference of the susceptor 28 are the same distanceaway from the RF coil, temperature uniformity can be readily establishedin the horizontal direction (within a row of substrates 30 on susceptor28). To achieve temperature uniformity in a vertical direction, the coilspacings are adjusted. The susceptor 28 is rotated at a rate ofapproximately 3 r.p.m. by motor 54 to maintain temperature uniformity ofi 5 C. at a temperature of 1 C. (which is the preferred temperatureselected for the aforedescribed reaction) over the entirecircumferential surface area of susceptor 28. For a more'completedescription of the structural details of the graphite susceptor 28,reference 7 is made to the aforementioned patent.

EXAMPLE In order to show an example of the operation and resultsachieved by the instant invention, the following description of thereactors operation and performance is provided.

The basic operating procedure of the instant invention is best describedin terms of the specific example of its operation as already referred toabovei.e., the hydrogen reduction of silicon tetrachloride.

Substrates 30, highly polished semiconductor wafers, are

loaded onto graphite susceptor 28 while bottom plate 16 is in thepreviously referred to lowered position. During this time, it may bedesirable to allow a nominal flow of inert gas, such as argon, to enterinlet tube 34 in order to maintain chamber 18 in a relatively cleancondition. Bottom plate 16 is then raised in order to close reactor 10for the deposition process. Chamber 18 is then purged for about oneminute by an inert gas, preferably argon, which is maintained at anydesirable flow rate which will insure adequate purging. Due to the highcost of argon, it is acceptable to utilize a purge rate of aboutone-tenth that of the reactant gases to be referred to later. The

rate used in the preferred embodiment should be sufficient to produce astreaming velocity in excess of the diffusion velocity for impurities inthe purging gas.

As the purge gas passes into plenum 36, it is uniformly dis tributedacross the surface of gas distribution baffle 38 providing a backpressure of about 2-4 psi. and a substantially planar velocity frontwithin chamber 18. Due to the relatively wide chamber cross section, ascompared with its length, the formation of a boundary layer, caused byfrictional contact between gas flowing through the reaction chamber andthe internal surfaces of quartz cylinder 12, is for all practicalpurposes, insignificant.

Because the purged gas enters chamber 18 with a planar velocity frontand because of the low gas resistance presented by susceptor 28,reaction chamber 18 is effectively purged in a very short period oftime.

After the chamber has been purged, the inert purge gas is replaced byhydrogen at a flow rate of about liters per minute for a period of about2 minutes to displace the purge gas and establish a total hydrogenambient for the vapor deposition reaction. This rate will produce astreaming velocity in excess of the diffusion velocity for impurities inthe hydrogen gas. The RF heating coils are energized while additionalhydrogen is passed through the chamber for about 7 minutes while thesubstrates are raised to the reaction temperature of 1 130 5 C., Justprior to admission the reactant gas flow is vented to purge the feedsystem and establish inch long susceptor the SiCl, is admitted to thereaction chamber in a hydrogen carrier at a rate of about 150 liters perminute in a SiCl /l-l ratio of about 0.01 for 6-14 minutes dependingupon the film thickness desired. In general, higher streaming velocitiesare required for longer susceptors.

The gas distribution baffle 38 and exit gas pressure baffle 42 act onthe reactant gases in the same manner as described above with referenceto the purge gas. Additionally, due to the fact that the reactant gasconcentration is substantially equal throughout the cross-sectional areaof the chamber, because of the relatively short length of susceptor 28,uniquely uniform deposition of reaction byproducts are obtained.

After the desired deposition time has elapsed hydrogen alone is passedthrough the chamber for about seconds to remove all traces of SiCl,

The RF power is then turned off and the substrates are cooled inhydrogen for about 6 minutes. Finally, the hydrogen is purged from thechamber with argon which further cools the substrates for about 2minutes. The reactor is opened and the coated substrates are removedfrom the susceptor.

A summary of the improvements achieved by the novel inlet and exitsystem of the subject invention, as compared with the prior art barrelreactor is given below.

The dust particle count of particles( greater than one-half micron) inthe chamber, as determined by a commercial dust counter, is about I00particles/ft". This is a 1,000 to l reduction from the count of 100,000particles/ftFas found in a reactor not equipped with the novel inlet andexit system.

The uniformity of deposit, as determined by the infrared interferencetechnique, for a o-micron film, previously 0.5 microns on a singlesubstrate, was reduced to i 0.1 microns for all substrates within thechamber.

The presence of spikes found on substrates was reduced from about 80 to100 per substrate to about one or two per substrate.

The duty cyclefor the entire deposition operation was reduced by afactor of from two to three times that required by prior art reactorsdue primarily to the efficient purging action 0f h r a atee xelqe txfrerr In summary, what has been disclosed is a novel structure for a vapordeposition reactor which significantly improves the quality of vapordeposition products. A structure which enables shortened duty cycles dueto more efficient purging of the reaction chamber both before and afterdeposition. Such a reactor includes a gas distribution baffle whichdelivers gases to the reaction chamber uniformly throughout itshorizontal cross section and a pressure baffle which assures uniformremoval of the gases from each portion of the horizontal crosss qn ssentthsqheslbsr at r n fqrmratst.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

hats c aimed. s-

ll. Apparatus for performing substrate surfaces utilizing gaseous phasematerials, comprismg:

a reaction chamber having a longitudinal axis; a substrate holder formaintaining substrate surfaces substantially parallel to saidlongitudinal axis; heating means for uniformly heating substratesurfaces to the reaction temperature; gaseous phase inlet means locatedat one end of said equilibrium flow before it is injected into thereactor. For a 7- i chamber comprising: a gas distribution baffle,forming a plenum, said baffle extending substantially throughout thecross-sectional area of said chamber, said baffle capable of providingsufficient gas resistance to develop substantially uniform back pressureacross said baffle, and said baffle also capable of deliveringsubstantially uniform mass flow into said chamber with a planar velocityfront, said velocity from moving parallel to said chamber axis and saidsubstrate surfaces; and a gaseous phase exit pressure baffle located atthe other end of said chamber and extending over substantially all ofthe cross-sectional area of said chamber, said exit baffle capable ofproviding substantially uniform gas resistance for maintaining a uniformmass flow rate per unit area across said other end of said chamber toprevent recirculation of the gaseous phase materials and reactionbyproducts in said chamber.

2. Apparatus as defined in claim 1 wherein said gas distribution baffleand said exit pressure baffle are perforated steel plates.

3. Apparatus as defined in claim ll wherein said gas distribution baffleis a sintered steel plate and said exit pressure baffle is a perforatedsteel plate.

4. Apparatus as described in claim 1 wherein the gas resistance of saidexit pressure baffle is about one-twentieth that of said gasdistribution baffle.

5. Apparatus as defined in claim 1 wherein said substrate holder is agraphite susceptor.

6. Apparatus as defined in claim 1 wherein said substrate holder issubstantially in the form of a hollow right circular cylinder.

7. Apparatus as defined in claim 6 wherein said heating means is an RFcoil for inductively coupling energy to said substrate holder.

8. Apparatus as described in claim 7 wherein said substrate holder isrotated in said chamber to insure uniform heating of said substratesurfaces.

9. Apparatus as claimed in claim l wherein there is provided a heatshield mounted between said gaseous phase inlet means and said substrateholder to protect said gas distribution baffle from energy radiated bysaid substrate holder.

110. in a vapor transport reactor including a reaction chamber having alongitudinal axis, a substrate holder for holding substrates havingreaction surfaces, heating means for heating means for heatingsubstrates to a reaction temperature, gaseous phase inlet means andgaseous phase exit means, the improvement comprising:

gaseous phase inlet means located at one end of the reaction chambercomprising: a gas distribution baffle forming a plenum, said baffleextending substantially throughout the cross-sectional area of thechamber, said baffle capable of providing sufiicient gas resistance togaseous phase material to develop substantially uniform back pressureacross said baffle, and said baffle also capable of deliveringsubstantially uniform mass flow into the chamber, said flow having asubstantially planar velocity front moving parallel to the longitudinalaxis of the chamber and the substrate surfaces; and

gaseous phase exit means comprising: an exit pressure baffle located atthe other end of the chamber and extending over substantially all of thecross-sectional area of the chamber, said exit pressure baffle capableof providing substantially uniform gas resistance to gaseous phasematerial in the chamber to maintain a uniform mass flow rate per unitarea across the chamber to prevent recirculation of gaseous phasematerials and reaction byproducts.

2. Apparatus as defined in claim 1 wherein said gas distribution baffleand said exit pressure baffle are perforated steel plates.
 3. Apparatusas defined in claim 1 wherein said gas distribution baffle is a sinteredsteel plate and said exit pressure baffle is a perforated steel plate.4. Apparatus as described in claim 1 wherein the gas resistance of saidexit pressure baffle is about one-twentieth that of said gasdistribution baffle.
 5. Apparatus as defined in claim 1 wherein saidsubstrate holder is a graphite susceptor.
 6. Apparatus as defined inclaim 1 wherein said substrate holder is substantially in the form of ahollow right circular cylinder.
 7. Apparatus as defined in claim 6wherein said heating means is an RF coil for inductively coupling energyto said substrate holder.
 8. Apparatus as described in claim 7 whereinsaid substrate holder is rotated in said chamber to insure uniformheating of said substrate surfaces.
 9. Apparatus as claimed in claim 1wherein there is provided a heat shield mounted between said gaseousphase inlet means and said substrate holder to protect said gasdistribution baffle from energy radiated by said substrate holder. 10.In a vapor transport reactor including a reaction chamber having alongitudinal axis, a substrate holder for holding substrates havingreaction surfaces, heating means for heating means for heatingsubstrates to a reaction temperature, gaseous phase inlet means andgaseous phasE exit means, the improvement comprising: gaseous phaseinlet means located at one end of the reaction chamber comprising: a gasdistribution baffle forming a plenum, said baffle extendingsubstantially throughout the cross-sectional area of the chamber, saidbaffle capable of providing sufficient gas resistance to gaseous phasematerial to develop substantially uniform back pressure across saidbaffle, and said baffle also capable of delivering substantially uniformmass flow into the chamber, said flow having a substantially planarvelocity front moving parallel to the longitudinal axis of the chamberand the substrate surfaces; and gaseous phase exit means comprising: anexit pressure baffle located at the other end of the chamber andextending over substantially all of the cross-sectional area of thechamber, said exit pressure baffle capable of providing substantiallyuniform gas resistance to gaseous phase material in the chamber tomaintain a uniform mass flow rate per unit area across the chamber toprevent recirculation of gaseous phase materials and reactionbyproducts.